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# Relations

This command opens the Relation Design window, which allows you to define relationships between various database tables.

Here you can link together tables from the current database through common data fields. Click the New Relation icon to create the relationships, or simply drag-and-drop with the mouse.

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In a database file window, choose Tools - Relationships.

This function is only available if you are working with a relational database.

When you choose Tools - Relationships, a window opens in which all the existing relationships between the tables of the current database are shown. If no relationships have been defined, or if you want to relate other tables of the database to each other, then click on the Add Tables icon. The Add Tables dialog opens in which you can select the tables with which to create a relation.

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If the Relation Design window is open, the selected tables cannot be modified, even in Table Design mode. This ensures that tables are not changed while the relations are being created.

The selected tables are shown in the top area of the relation design view. You can close a table window through the context menu or with the Delete key.

#### Move table and modify table size

You can resize and arrange the tables according to your preferences. To move tables, drag the upper border to the desired position. Enlarge or reduce the size in which the table is displayed by positioning the mouse cursor on a border or on a corner and dragging the table until it is the desired size.

## Primary key and foreign keys

If you want to define a relation among the various tables, you should enter a primary key that uniquely identifies a data field of an existing table. You can refer to the primary key from other tables to access the data of this table. All data fields referring to this primary key will be identified as a foreign key.

All data fields referring to a primary key will be identified in the table window by a small key symbol.

## Define relations

All existing relations are shown in the relations windows by a line that connects the primary and foreign key fields. You can add a relation by using drag-and-drop to drop the field of one table onto the field of the other table. A relation is removed again by selecting it and pressing the Delete key.

Alternatively, you can also click the New Relation icon in the top area of the relation field and define the relation between two tables in the Relations dialog.

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If you use LibreOfficeDev as the front-end for a relational database, the creation and deletion of relationships is not placed in an intermediate memory by LibreOfficeDev, but is forwarded directly to the database.

By double-clicking a connection line, you can assign certain properties to the relation. The Relations dialog opens.

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